You'll still need to support 32 and 64 bits so it isn't completely painless but it's a lot better than trying to cope with all the flavours.
That's not simple at all. If I want to integrate properly with your desktop, do I write my code against gnome or KDE?
If I statically link against an older (or newer) version of gnome or KDE, will it even interoperate correctly with whatever the user has running on their desktop?
If there's a security vulnerability in what should be a base system library, does every single vendor have to track those issues and release updates to their applications?
No. The right way to support binary compatibility is to define a compatible, stable API and ABI and then support that ABI/API across OS releases and updates.
With that I fully agree. But I think if the last decade is any indication that in the linux world we are still at least a decade away from achieving that, even though there are plenty of efforts in that direction.
All this freedom is a mixed blessing.
The wider point is tho', that criticizing a walled garden because it doesn't do something you want, and criticizing it on principle may overlap, but they aren't the same issue at all.
I personally quite like that Facebook is walled off from the real Internet... Go browse the comments on Youtube if you want to see what that's like.
Social networks are mainly places for people socialize with friends. When people get onto youtube and start flaming people they are usually not directly flaming their friends (or at least not doing so from a username that their friends will recognize). Things like privacy settings, friend lists, etc are what help to regulate something like Facebook.
If there was a well-defined protocol for pulling/pushing just the information that was needed for a particular profile (say having all of my friends updates pushed to my account on whichever server it's being hosted), then it doesn't necessarily open up this decentralized social network to youtube-style garbage. For you to see the youtube-style garbage you would need to accept the troll onto your network. And even after they were exposed as a troll, you could banish them.